Priority is claimed to Korean Patent Application No. 10-2004-0075969, filed on Sep. 22, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a flat lamp, and more particularly, to a flat lamp that can reduce a discharge voltage and improve luminous efficiency.
2. Description of the Related Art
Flat lamps have developed as back-lights of liquid crystal displays (LCD). They include a surface discharge type or a facing discharge type flat lamp type, in which a whole lower portion of the light emitting surface is discharge space, in consideration of luminous efficiency and uniformity of brightness. These are regarded as improvements to a conventional edge-light type or a direct-light type flat lamp which uses a cold cathode fluorescent lamp. The surface discharge flat lamp has an advantage of a stable discharge characteristic compared to a facing discharge flat lamp, but brightness is inferior to the facing discharge flat lamp.
FIG. 1 is an exploded perspective view of a conventional surface discharge flat lamp. FIG. 2 is a partial cross-sectional view of the flat lamp of FIG. 1.
Referring to FIGS. 1 and 2, a lower substrate 10 and an upper substrate 20 are disposed facing each other with a predetermined distance by frames 16. A closed discharge space is formed by the frames 16 between the lower substrate 10 and the upper substrate 20. Conventionally, this space is filled with a discharge gas mixed with neon (Ne) gas and xenon (Xe) gas. A plurality of spacers 14 that defines a plurality of discharge cells 15 by defining the discharge spaces is disposed between the lower substrate 10 and the upper substrate 20. The spacers 14 support the lower substrate 10 and the upper substrate 20 and, at the same time, prevent crosstalk between the adjacent discharge cells 15.
A fluorescent layer 30 that generates visible light by being excited by ultraviolet rays generated by a discharge is formed on an inner side of the lower substrate 10 and the upper substrate 20 and both sides of the spacers 14. And, a plurality of discharge electrodes for generating a plasma discharge are formed on the lower substrate 10 and the upper substrate 20. More specifically, each of first and second lower electrodes 12a and 12b and first and second upper electrodes 22a and 22b are formed in pairs on an outside of the lower substrate 10 and the upper substrate 20, respectively. Here, the first electrodes 22a are connected to a first upper common line 23, and the second upper electrodes 22b are connected to a second upper common line 24. Also, the first lower electrodes 12a are connected to a first lower common line (not shown), and the second lower electrodes 12b are connected to a second lower common line (not shown). In the above configuration, no discharge occurs between the first lower electrode 12a and the first upper electrode 22a since the same potential is applied to the first lower electrode 12a and the first upper electrode 22a. Also, no discharge occurs between the second lower electrode 12b and the second upper electrode 22b since the same potential is applied to the second lower electrode 12b and the second upper electrode 22b. On the other hand, a surface discharge in a parallel direction to the lower substrate 10 and the upper substrate 20 since a predetermined potential difference is existed between the first lower electrode 12a and the first upper electrode 22a and between the second lower electrode 12b and the second upper electrode 22b, respectively.
However, in a flat lamp having above configuration, there is a problem of increasing the discharge voltage when a gap between the electrodes is increased, a partial pressure of the Xe gas is increased, or the pressure of the discharge gas is increased to increase the luminous efficiency.